1. Field of the Invention
The present invention relates to a method of extracting heat from manure, sewage mud, and other wet waste by combustion, the method comprising using a combined drying-, combustion-, and steam-condensing-process.
2. Description of the Prior Art
Organic waste such as for instance manure and sewage mud occurs in large quantities and often causes problems as a consequence of the content of vira, unpleasant smelling substances or dangerous toxicants. This implies that spreading of the organic waste in fields has been prohibited or connected with the risk of infection and inconveniences for the surroundings.
The wet waste contains a considerable amount of energy, which as for the manure alone corresponds to about a quarter of the energy annually consumed for heating in Denmark.
The extraction of heat from this waste is, however, difficult due to the high content of water, which implies that a direct combustion is impossible. Instead of combustion, biological methods for converting the substances may be employed, anaerobic conditions permitting generation of gas and aerobic conditions permitting generation of heat. These methods, however, require rather expensive plants, and in practice maximum about 30% of the total energy of the waste can be extracted.
By mixing sewage mud and household waste in an appropriate ratio, it is possible to combust the mud. However, the major part of the energy of the dry matter is used for evaporating the water and is thereby lost through the chimney.